This invention relates to a process for converting coal to gaseous products in a slagging type of coal gasifier or reactor. More particularly, the process relates to ensuring the forming and maintaining of heat insulating layers of solidified slag in locations between the combustion zone within the gasifier and metallic materials which are located near that zone.
Coal is commonly subjected to partial combustion, to produce gases which are useful as fuels and starting materials for chemical syntheses and the like, in a slagging gasifier. The combustion temperatures are usually kept at about 1500.degree. to 2700.degree. C. to convert the coal ash into a molten slag. The slagging coal gasifiers are generally the most flexible in terms of the variety of coal feedstocks which can be efficiently utilized. A significant proportion of the molten slag is continuously or intermittently removed from the bottom of the gasifier. Where desirable, additional portions of molten slag are produced by condensing the fly ash in the gaseous products and are flowed down within the walls of the reactor, for example, as described in U.S. Pat. No. 4,054,424.
In slagging coal gasifiers pulverized coal is introduced by means of one or more burners through which streams of pulverized coal, carrier gas and oxygen are injected into the combustion zone of the reactor. In general, it is necessary that some metallic materials, at least along the inner (or front) faces of such burners, be located near the combustion zone of the reactor. The inner walls of the reactor are usually composed of or lined with a refractory material such as a firebrick or other ceramic material. The faces of the burners are formed of heat resistant metals having high melting points and the burners are commonly provided with a water cooling system. The combustion zone is subjected to both the high temperatures and turbulent motion of the burning gases and liquefied and solidifying solid particles of coal, fly ash and molten slag. This provides a highly corrosive atmosphere adjacent to any nearby metallic surfaces and tends to corrode them at an undesirably high rate.